Brain CT Plain
A Complete Academic Guide to Non-Contrast CT of the Head
Clinical history, patient preparation, positioning, scan planning, scanning technique, image reconstruction, Siemens CT workflow, quality assessment, radiation safety and examination completion.
For CT Students, Radiographers and CT Technologists
Contents
- Introduction to Brain CT
- Clinical History and Terminology
- Patient Preparation
- Patient Positioning
- Scout and Scan Planning
- CT Head Plain Scanning Technique
- Siemens CT Operating Workflow
- Image Reconstruction and Windowing
- Basic Brain CT Anatomy
- Common CT Findings
- Image Quality Assessment
- Radiation Safety and ALARA
- PACS and Examination Completion
- Common Errors
- Complete Examination Sequence
- Viva and Revision Questions
Introduction to Brain CT
Computed tomography of the brain is one of the most frequently performed examinations in emergency and neurological imaging. A plain CT head examination uses X-rays and computer reconstruction to produce cross-sectional images of the skull and intracranial structures.
The examination is particularly useful when rapid assessment is required. It can demonstrate acute intracranial hemorrhage, skull fracture, mass effect, hydrocephalus and other important abnormalities. In emergency practice, the speed and availability of CT make it an important part of the initial evaluation of many neurological and traumatic conditions.
The CT technologist must understand that an examination does not begin when the patient lies on the CT table. It begins with the request form and clinical history. The technologist must identify the patient, understand the reason for the examination, prepare the patient appropriately, position the head accurately, select the correct protocol, plan the scan, acquire the images and evaluate technical quality before transferring the examination to PACS.
Clinical History and Terminology
Clinical history provides the medical context for the CT examination. The same anatomical region may be scanned for very different clinical reasons, and the reason for examination determines what the clinical team is attempting to evaluate.
Trauma
Trauma refers to physical injury produced by an external force. Head trauma may occur following a road traffic accident, fall, assault, sports injury or other mechanism. In traumatic cases, the clinical history should be reviewed carefully because information such as loss of consciousness, vomiting, seizure and mechanism of injury may be clinically important.
Headache
Headache, or cephalgia, refers to pain involving the head. CT is not automatically indicated for every headache. The clinical team may request CT when particular clinical features or red flags require rapid assessment for intracranial pathology.
Neurological Symptoms
Patients may be referred for CT because of weakness, altered consciousness, confusion, seizure, dizziness, speech disturbance or other neurological symptoms. The technologist should record and understand the information provided on the examination request.
Common Clinical Vocabulary
| Term | Meaning |
|---|---|
| Trauma | Physical injury caused by an external force. |
| RTA | Road traffic accident. |
| LOC | Loss of consciousness. |
| GCS | Glasgow Coma Scale, used clinically to assess level of consciousness. |
| CVA | Cerebrovascular accident, commonly referring to stroke. |
| Hemiparesis | Weakness affecting one side of the body. |
| Hemiplegia | Paralysis affecting one side of the body. |
| Syncope | Transient loss of consciousness and postural tone. |
| Vertigo | A sensation of movement or spinning. |
| Altered sensorium | Altered state or level of consciousness. |
| Mass effect | Compression or displacement of normal intracranial structures. |
| Midline shift | Displacement of normally central intracranial structures. |
| Hydrocephalus | Abnormal enlargement of the ventricular system associated with disturbed CSF dynamics. |
Intracranial Hemorrhage Terminology
The major types of intracranial hemorrhage encountered in CT education include epidural hematoma, subdural hematoma, subarachnoid hemorrhage, intracerebral hemorrhage and intraventricular hemorrhage. These terms describe the anatomical location of blood.
| Abbreviation | Full Term | General Location |
|---|---|---|
| EDH | Epidural / Extradural Hematoma | Between the skull and dura. |
| SDH | Subdural Hematoma | Between dura and arachnoid. |
| SAH | Subarachnoid Hemorrhage | Subarachnoid spaces. |
| ICH | Intracerebral Hemorrhage | Brain parenchyma. |
| IVH | Intraventricular Hemorrhage | Ventricular system. |
Patient Preparation
Proper preparation reduces preventable errors and helps the patient remain comfortable and still throughout the examination.
Patient Identification
Before beginning the examination, the technologist should verify the patient using the identification procedure required by the institution. Appropriate identifiers may include the patient's name, hospital identification number and date of birth. The information on the CT console should correspond with the patient physically present.
Correct identification is one of the most important parts of CT practice. A technically perfect examination performed on the wrong patient remains an unacceptable examination.
Review of the Examination Request
The request should be reviewed before the patient is positioned. The technologist should confirm the requested examination, clinical history and whether the examination is plain or contrast-enhanced. A request for CT head plain should not be confused with CT angiography, CT perfusion or contrast-enhanced brain CT.
Patient Explanation
The patient should be told what will happen. A simple explanation is usually adequate. The patient should understand that the head will be positioned in a support, the table will move through the scanner and the head must remain still during image acquisition.
Removal of Artifacts
Spectacles, earrings, hairpins and other external metallic objects around the head should be removed when practical and safe. Removable dental appliances may also be removed according to departmental practice. The purpose is to reduce avoidable metallic artifacts that can obscure intracranial structures.
Trauma Patient
Trauma patients require particular care. If cervical spine injury is suspected, unnecessary movement of the head and neck should be avoided. The patient should be managed according to the institution's trauma and immobilization pathway.
Pregnancy Consideration
Because CT uses ionizing radiation, pregnancy screening and radiation protection procedures should follow the applicable institutional policy. An indicated emergency examination should not simply be abandoned; appropriate clinical and radiation-safety procedures should be followed.
Patient Positioning
Correct positioning is essential because head rotation, tilt and incorrect centering can affect image appearance and technical quality.
Standard Position
For a routine adult CT head examination, the patient is generally positioned supine with the head first. The head is placed in the appropriate head holder and positioned close to the scanner isocenter. The patient should be comfortable and movement should be minimized.
Mid-Sagittal Alignment
The midsagittal plane of the patient's head should be aligned with the scanner's center. Excessive rotation can create apparent asymmetry between the cerebral hemispheres and can make comparison of structures more difficult.
Head Support and Immobilization
The head should be supported in a stable position. Foam supports or other appropriate immobilization devices may be used according to departmental practice. Immobilization should be sufficient to reduce movement without causing unnecessary discomfort.
Isocenter
The anatomical region being examined should be positioned appropriately relative to the scanner isocenter. Correct centering contributes to consistent image quality and dose optimization.
Positioning Errors
| Error | Possible Effect |
|---|---|
| Head rotation | Apparent asymmetry of intracranial structures. |
| Head tilt | Changes anatomical orientation. |
| Poor vertical centering | May affect image quality and dose efficiency. |
| Patient movement | Motion artifact and reduced diagnostic quality. |
Scout and Scan Planning
The scout, or topogram/localizer, provides the planning image used to determine the acquisition range and evaluate patient positioning.
Acquiring the Scout
After the patient is positioned, the appropriate localizer is obtained according to the scanner's workflow. The technologist should inspect the scout before starting the diagnostic acquisition.
Scan Coverage
The routine head examination should include the required intracranial anatomy from the skull base through the vertex. The complete bony cranium should be included according to the examination protocol.
Why Planning Is Important
The planning stage is not merely a preliminary step. If the scan range is incorrectly positioned, clinically important anatomy may be omitted. The technologist should therefore inspect the proposed acquisition carefully before starting the exposure.
CT Head Plain Scanning Technique
A CT head protocol must be selected according to the scanner, patient population and clinical task. There is no single set of exposure parameters that should be copied to every CT scanner.
Tube Voltage
Tube voltage, expressed in kilovolts, influences the energy of the X-ray beam. The selected value should be based on the approved CT protocol and the capabilities of the particular scanner.
Tube Current and Exposure
Tube current and exposure settings influence photon production and image noise. Modern CT systems may use automatic exposure-control methods, depending on the scanner and protocol.
Collimation
Collimation describes the detector configuration and effective width of the X-ray beam used during acquisition. The appropriate configuration depends on the scanner's detector system.
Rotation Time
Rotation time is the time required for the X-ray tube to complete one rotation around the patient. It contributes to acquisition speed and interacts with other exposure parameters.
Pitch
Pitch is primarily relevant to helical acquisition. It describes the relationship between table movement and the total nominal beam width. Its appropriate value is determined by the selected protocol.
Field of View
The field of view determines the anatomical area represented during image reconstruction. For a head examination, it should be selected appropriately for the skull and brain.
Slice Thickness
Slice thickness influences spatial resolution, image noise and the ability to evaluate structures in different planes. The required reconstruction thickness should follow the institutional protocol.
Important Protocol Principle
Siemens CT Operating Workflow
The following sequence describes a general Siemens SOMATOM-style workflow. Exact screen names, buttons and protocol names differ among scanner models and software versions.
Step 1 — Prepare the CT System
Before beginning the patient examination, confirm that the CT system is operational and ready. Required daily quality-control or calibration procedures should be completed according to departmental policy and manufacturer recommendations.
Step 2 — Patient Registration
Open the patient registration area of the Siemens CT console and create the examination. Enter the required patient information accurately. The patient's identification information should correspond with the physical patient.
Step 3 — Enter Patient Information
Depending on the system configuration, information may include patient name, patient identification number, date of birth, sex, accession number and referring information. Clinical information should be entered or confirmed according to departmental workflow.
Step 4 — Select the Examination
Select the appropriate head or brain examination and verify that the requested examination is a plain, non-contrast CT head. Do not accidentally select CTA, CTV, CT perfusion or contrast-enhanced brain protocols.
Step 5 — Select the Approved Protocol
Select the institution-approved head protocol appropriate for the patient. Adult, pediatric and specialized examinations may use different protocols.
Step 6 — Position the Patient
Place the patient supine, generally head first, and position the head in the appropriate support. Align the patient's head and center the anatomy using the scanner positioning system.
Step 7 — Laser Alignment
Use the scanner laser alignment system to establish the patient's relationship to the gantry isocenter. Check the head for rotation and tilt before moving to the next stage.
Step 8 — Acquire the Scout
Acquire the appropriate localizer or topogram. Examine the resulting scout for patient position, centering and anatomical coverage.
Step 9 — Plan the Acquisition
Plan the diagnostic acquisition according to the approved head protocol. The required intracranial anatomy should be covered from the skull base through the vertex.
Step 10 — Review the Parameters
Before exposure, review the selected acquisition parameters and reconstruction settings. Verify that the correct protocol has been selected and that no unauthorized parameter changes have been made.
Step 11 — Give the Patient Final Instructions
Tell the patient to keep the head completely still. If the patient is unconscious or unable to cooperate, appropriate clinical support and immobilization should be used according to local practice.
Step 12 — Start the Scan
Start the approved diagnostic acquisition. During the scan, continue to observe the patient and remain prepared to respond to an emergency.
Step 13 — Reconstruction
Generate the required standard brain reconstruction. Additional reconstructions, including bone algorithms, should be produced when required by the clinical indication or departmental protocol.
Step 14 — Review the Images
The technologist should review the images for coverage, motion, artifacts, correct reconstruction and correct patient/study identification. This is a technical quality check and does not replace radiologist interpretation.
Step 15 — Send to PACS
After confirming technical adequacy, send the examination to the appropriate PACS destination. Confirm that the study is associated with the correct patient and examination.
Step 16 — Complete the Examination
Complete the required documentation and follow the institutional process for radiologist interpretation and urgent-result communication.
Image Reconstruction and Windowing
The CT scanner acquires projection data, which are reconstructed into cross-sectional images. Different reconstruction algorithms and display settings allow the same examination to be evaluated for different clinical purposes.
Brain Reconstruction
The standard brain reconstruction is optimized for intracranial soft tissue evaluation. It allows assessment of the brain parenchyma, gray-white differentiation, ventricles, hemorrhage, edema and mass effect.
Bone Reconstruction
A sharper reconstruction algorithm provides greater emphasis on high-contrast structures such as bone. Bone reconstructions are useful when evaluating the calvarium, skull base and suspected fractures.
Window Width and Window Level
Window width and window level determine how CT attenuation values are displayed on the monitor. A brain window is optimized for soft tissue, while a bone window is optimized for osseous structures.
| Display | Main Purpose |
|---|---|
| Brain / Soft Tissue Window | Brain parenchyma, hemorrhage, edema, ventricles and mass effect. |
| Bone Window | Skull, skull base and fractures. |
Basic Brain CT Anatomy
A technologist should have a working knowledge of normal anatomy in order to recognize whether the examination has been adequately positioned and whether all required anatomical regions have been included.
Cerebral Hemispheres
The cerebrum is divided into right and left cerebral hemispheres. Normal CT images should demonstrate the expected bilateral anatomical relationships.
Cerebral Lobes
The major cerebral lobes are the frontal, parietal, temporal and occipital lobes. Their appearance changes as the axial images move from the skull base toward the vertex.
Deep Gray Matter
The basal ganglia and thalami are important deep structures. Their recognition is useful when assessing symmetry and brain anatomy.
Ventricular System
The ventricular system includes the lateral ventricles, third ventricle and fourth ventricle. Their size and configuration are important when considering hydrocephalus and mass effect.
Posterior Fossa
The posterior fossa contains the cerebellum and brainstem. It is particularly important to ensure that the inferior portions of the brain are included in the examination.
| Structure | Basic Location / Description |
|---|---|
| Frontal lobe | Anterior portion of the cerebrum. |
| Parietal lobe | Superior and posterior cerebral region. |
| Temporal lobe | Lateral and inferior cerebral region. |
| Occipital lobe | Posterior cerebral region. |
| Basal ganglia | Deep gray matter structures. |
| Thalami | Paired deep gray matter structures. |
| Ventricles | CSF-containing ventricular system. |
| Cerebellum | Posterior fossa structure. |
| Brainstem | Midbrain, pons and medulla. |
Common CT Findings
This section introduces common terminology used in brain CT. It is intended for academic recognition and should not be used by a technologist as a substitute for formal diagnostic interpretation.
Intracranial Hemorrhage
Acute blood commonly appears relatively hyperdense compared with normal brain on non-contrast CT. The appearance and location depend on the type of hemorrhage.
| Morphological Classification of Intracranial Hemorrhage |
|---|
| Epidural Hemorrhage (EDH) |
| Subdural Hemorrhage (SDH) |
| Subarachnoid Hemorrhage (SAH) |
| Intracerebral / Intraparenchymal Hemorrhage (ICH) |
| Intraventricular Hemorrhage (IVH) |
| Cerebellar Hemorrhage |
| Brainstem Hemorrhage |
| Mixed / Multifocal Hemorrhage |
Mass Effect
Mass effect refers to displacement or compression of normal brain structures. It may be associated with sulcal effacement, ventricular compression or displacement of midline structures.
| Classification Mass Effect |
|---|
| Sulcal Effacement |
| Ventricular Compression |
| Midline Shift |
| Cisternal Effacement |
| Subfalcine Herniation |
| Uncal Herniation |
| Transtentorial Herniation |
| Tonsillar Herniation |
| Obstructive Hydrocephalus |
Midline Shift
Midline shift occurs when normally central structures are displaced from their expected position. It may occur as a result of hemorrhage, mass lesion, edema or other space-occupying processes.
| Midline Shift |
|---|
| Mild Midline Shift (<5 mm) |
| Moderate Midline Shift (5–10 mm) |
| Severe Midline Shift (>10 mm) |
| Subfalcine Shift |
| Midline Shift with Herniation |
Cerebral Edema
Cerebral edema represents swelling of brain tissue. Depending on its severity, it can result in reduced differentiation, sulcal effacement, ventricular compression and other signs of increased intracranial pressure.
| Morphological Classification of Cerebral Edema |
|---|
| Mild Cerebral Edema |
| Moderate Cerebral Edema |
| Severe / Diffuse Cerebral Edema |
| Focal Cerebral Edema |
| Diffuse Cerebral Edema |
| Cerebral Edema with Mass Effect |
Hydrocephalus
Hydrocephalus refers to abnormal enlargement of the ventricular system associated with disturbed CSF circulation, absorption or production.
| Morphological Classification of Hydrocephalus |
|---|
| No Hydrocephalus |
| Mild Hydrocephalus |
| Moderate Hydrocephalus |
| Severe Hydrocephalus |
| Obstructive Hydrocephalus |
| Communicating Hydrocephalus |
| Acute Hydrocephalus |
| Chronic Hydrocephalus |
| Hydrocephalus with Periventricular Edema |
Skull Fracture
Skull fractures are more readily evaluated using appropriate bone reconstructions. Trauma history should be correlated with the appearance of the calvarium and skull base.
| Morphological Classification of Skull Fracture |
|---|
| No Skull Fracture |
| Linear Skull Fracture |
| Depressed Skull Fracture |
| Comminuted Skull Fracture |
| Basilar Skull Fracture |
| Open Skull Fracture |
| Closed Skull Fracture |
| Multiple Skull Fractures |
Image Quality Assessment
After acquisition, the technologist should perform a systematic technical review before completing the examination.
Coverage
First determine whether the complete required anatomical region has been included. The examination should extend through the appropriate skull base and vertex according to protocol.
Patient Motion
Motion can produce blurring or duplicated anatomical structures. The technologist should determine whether motion significantly affects diagnostic quality and follow the department's approved procedure when repeat acquisition is considered.
Metallic Artifact
Dental materials and other metallic objects can produce streak artifacts, particularly around the skull base. External removable metal should be removed when practical.
Series and Reconstruction
The required brain reconstruction should be present and correctly labeled. Additional series, such as bone reconstruction, should be included when required by the protocol or clinical indication.
Technical Quality Checklist
| Check | Question |
|---|---|
| Patient | Is this the correct patient and examination? |
| Position | Is the head adequately centered and aligned? |
| Coverage | Is the complete required anatomy included? |
| Motion | Is the examination sufficiently free from motion? |
| Artifacts | Are artifacts acceptable for the clinical task? |
| Reconstruction | Are the required image series present? |
| Labeling | Are the patient and series labels correct? |
| PACS | Will the correct examination be sent to the correct destination? |
Radiation Safety and ALARA
CT uses ionizing radiation. Radiation protection therefore forms an essential part of CT practice.
ALARA
ALARA means As Low As Reasonably Achievable. In CT, the principle means that radiation exposure should be optimized while maintaining sufficient image quality for the clinical purpose.
The objective is not to reduce radiation at any cost. An excessively low exposure that produces nondiagnostic images may lead to repeat scanning and therefore additional exposure. The correct approach is protocol optimization.
Practical Radiation-Safety Principles
The technologist should use the correct protocol, avoid unnecessary repeat examinations, select patient-appropriate protocols and follow the radiation-safety procedures established by the institution and applicable regulations.
Pediatric Patients
Children should not simply be scanned using an adult CT head protocol. Pediatric protocols are designed to account for differences in patient size and radiation sensitivity.
PACS and Examination Completion
The CT examination is not complete when the scanner stops. The images must be reconstructed, reviewed, correctly identified and transferred to the appropriate image-management system.
Before Sending to PACS
The technologist should verify the patient name, patient identification number, examination description, accession information and series labels. The images should be checked for coverage, motion and major technical artifacts.
Transfer to PACS
The completed examination is sent to the designated PACS destination. The technologist should verify that the study has transferred correctly and is associated with the correct patient.
Final Completion
After the study is successfully transferred, the technologist completes the required documentation and follows the institution's procedure for radiologist interpretation and communication of urgent findings.
Common Errors and Their Prevention
| Common Error | Prevention |
|---|---|
| Wrong patient | Use the required patient-identification procedure before scanning. |
| Wrong examination | Compare the request with the selected protocol. |
| Incorrect positioning | Check head alignment, rotation and centering before the scout. |
| Patient movement | Explain the importance of remaining still and immobilize appropriately. |
| Incomplete scan range | Inspect the scout and planned acquisition before starting. |
| Metallic artifact | Remove external metal where practical. |
| Incorrect reconstruction | Verify the required brain and other protocol-specific series. |
| Incorrect PACS destination | Verify patient and study information before transfer. |
Complete CT Head Plain Examination Sequence
The following sequence provides a simple mental model for the complete examination.
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2. Identify patient
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3. Review clinical history
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4. Confirm CT Head Plain
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5. Prepare patient
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6. Position supine / head first
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7. Center and align head
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8. Acquire scout
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9. Plan scan range
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10. Verify approved protocol
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11. Acquire CT
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12. Reconstruct images
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13. Review technical quality
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14. Send to PACS
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15. Verify transfer
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16. Complete examination
Memory Formula
A simple way to remember the workflow is:
REGISTER → PREPARE → POSITION → PLAN → SCAN → RECONSTRUCT → CHECK → PACS
Viva and Revision Questions
1. What is a plain CT head?
A plain CT head is a non-contrast CT examination of the head and brain.
2. What is the usual patient position?
The patient is generally positioned supine, head first, with the head supported, centered and immobilized.
3. Why is patient centering important?
Correct centering supports consistent image quality and radiation-dose optimization.
4. Why is a scout image obtained?
The scout provides a localizer used to evaluate positioning and plan the diagnostic acquisition.
5. What is the usual anatomical coverage?
The required head examination should include the appropriate anatomy from the skull base through the vertex.
6. What is a brain window?
A display setting optimized for evaluation of intracranial soft tissue.
7. What is a bone window?
A display setting optimized for evaluation of osseous structures.
8. What does ALARA mean?
As Low As Reasonably Achievable. It is the principle of optimizing radiation exposure while maintaining appropriate diagnostic quality.
9. What is EDH?
Epidural or extradural hematoma.
10. What is SDH?
Subdural hematoma.
11. What is SAH?
Subarachnoid hemorrhage.
12. What should be done when significant motion occurs?
The technologist should determine whether image quality is compromised and follow the institution's approved procedure for correction or repeat acquisition when justified.
13. Does a technologist provide the final diagnosis?
No. The technologist performs the examination according to approved procedures and performs technical quality control. Formal diagnostic interpretation is performed by the appropriately qualified interpreting physician.
Summary
A high-quality CT head examination is the result of a controlled, systematic workflow.
The process begins with understanding the clinical history and confirming the correct examination. Patient preparation follows, including identification, explanation, artifact removal and appropriate trauma precautions. The patient is then positioned carefully, with the head centered and immobilized.
The scout is acquired and inspected before the diagnostic acquisition is planned. The technologist verifies the approved protocol and performs the scan using scanner-specific parameters. The resulting data are reconstructed using the appropriate algorithms and reviewed for technical adequacy.
Finally, the completed study is correctly labeled and transferred to PACS. The technologist then completes the examination according to departmental procedure and the study proceeds to formal interpretation.
Use of This Academic Guide
This material is intended for education and training. It does not replace the manufacturer's operator manual, institutional CT protocol, radiologist instructions, medical-physics guidance, radiation-safety requirements or applicable regulations.
Siemens SOMATOM systems differ in model, detector configuration, software version and installed options. Consequently, exact console buttons, protocol names and exposure parameters must be verified on the specific scanner used in the department.
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